K. E. Buck, W. R. Martini, Wm. T. Beale, G. M. Benson, myself and others have invented various thermally driven piston devices utilizing one or more free or semi-free pistons and alternate heating and cooling of a gas or other compressible fluid to develop a pulsating fluid pressure for pumping a fluid or otherwise driving a fluid driven load. An artificial heart, a free piston linear alternator, a fluid driven rotary motor for driving a rotary alternator, and fluid pumping for cooling purposes are several examples of uses or loads for such devices.
My inventions in this field are described primarily in my U.S. Pat. Nos. Re. 27,740, 3,767,325, 3,782,859, 3,807,904, and 3,899,888, and in my U.S. Pat. No. 4,012,910 entitled "Thermally Driven Piston Apparatus Having An Angled Cylinder Bypass Directing Fluid Into A Thermal Lag Heating Chamber Beyond The Bypass", Ser. No. 592,895, filed July 3, 1975, of which application the present application is a Continuation-In-Part. In my inventions, the free piston is driven by fluid heated in a thermal lag heating chamber, and this is one of the differences between my inventions in this field and the inventions by others; this feature facilitates a very simple thermocompressor design having a single free piston as its only moving part. In my Stirling type inventions (the second and third patents noted above and my U.S. Pat. No. 4,012,910), the device can be simplified so that the thermal lag heating chamber, which is located beyond a cylinder bypass containing a regenerator, serves not only to provide thermal lag heating for driving the free piston during piston rebound but also serves as a Stirling type heating chamber for heating the gas flowing through the bypass into the hot end of the cylinder during piston coasting.
However, since my thermal lag heating chamber is disposed beyond the bypass, it would probably be difficult with the Stirling type configurations disclosed in my patents to get substantially all of the fluid which flows through the bypass into the hot end of the cylinder to enter and flow through the thermal lag heating chamber for heating therein while the piston is coasting upwardly in the bypass region of the cylinder, the apparatus possibly therefore being operationally inefficient and perhaps having a low specific power output. In my above-mentioned U.S. Pat. No. 4,012,910, this problem was partially solved by various design features which included angling of the hot bypass conduit towards the heating chamber inlet port so that the nozzle effect of the hot bypass conduit tended to keep the fluid in a substantially defined stream which entered a heating chamber inlet port of a heating chamber inlet conduit. The fluid thence flowed into and through the heating chamber and returned to the hot end of the cylinder via a heating chamber outlet conduit. However, this fluid flow was retarded slightly by fluid drag in the heating chamber and its inlet and outlet conduits. Also, the stream of fluid flowing within the hot end of the cylinder toward the inlet port tends to enlarge and become more diffuse, depending on such factors as the inertia and diffusivity of the working fluid. Thus the limited range of the nozzle effect in combination with the fluid drag may, in my U.S. Pat. No. 4,012,910, cause a substantial amount of the fluid to miss the inlet port and not traverse the heating chamber. For example, in my U.S. Pat. No. 4,012,910 the heating chamber inlet port may be in the cylinder side-wall or in the flat end-wall and approximately on the opposite side of the cylinder axis from the hot bypass conduit, i.e., a distance from the hot bypass conduit which is approximately equal to one cylinder diameter.
In view of the above, it would be desirable to substantially decrease the distance between the hot bypass conduit and the heating chamber inlet port of the device of my U.S. Pat. No. 4,012,910 so that, for any given working fluid, a substantially greater portion of the fluid flowing out of the hot bypass conduit enters and traverses the heating chamber while the piston is coasting upwardly in the bypass region of the cylinder, thereby augmenting the pressure increase during this portion of the cycle of the thermocompressor.